Note: Descriptions are shown in the official language in which they were submitted.
CA 02218104 1997-10-10
LOW VIS~OSIIY POLYI~RETEk~E PREPOLY~IER ~OHPOSI~IO~i
T~e i~ve~tio~ ~elates to a ~ow viscosity polyuretha~e prepclymer compQSi~iOn~
Polyuretha~e prepoly~ers are e~g. used as edge ~nd surf ace fi~ishi~g -age~ts
for materials~ part~ulz~ly those havi~g a oertal~ ~at~ral da~pnes~ or
ab$orb molsture fra~ t~e enviro~ent~ Typic~l exzmples are mould~nss,
boar~s7 etc. made from w~od, ~ooden ma~erials or other natural ~brous ma~-
erials. In order tc avoid solvent ~aste a~d e~ssions increasi~g use is
bein~ made of polymer systems cont~tuiug li~tle or ~o solTJen~. Such poly-
~ers are ge~erally kno~Tn aud are described ~n the l~terature.
O~e of the vital prereq~isites for the seall~ or ~ishin~ (also Prim~n~ or
grou~ding) i~ a~ ~dequately good ~Te~ab~llty and Pe~etr~tabiilty via the
pores into the substrate ~ the par~lcul~r ma~erlal. AS a functio~ of the
a~m and p~rpose of t~e sealing or finish~ng, a polymer viscosity of 50 to
120 mPas ~e 20~~ ~s expected. H~therto use has been ~ade of one-component
pol~rethane ~o~ g masses ~DE 33 39 683 Al? EP 0 076 956 Al, US 5 126
4~1 Cl)7 ~h1oh are diluted dow~ ~a the desired ~-lsoosity with s~ghtly
polar to ~polar solve~uts, e.~ a~lphatic es~ers, such as 571ycOl or ethyl
acetate a~d arom~t~c ~y~rocar~ons, such as tolue~le, ~ylene, etC. It is
also known (E~ 0 0~7 195 Al) ~o ~nc~rporate l~to a prepolymer a ~on-vol~ile
~oLve~, na2ely a Cpecif~c l~ctone, in order to red~c~ the vlscosity~
sol~ds COhce~tration of 30 to 7~, mAi~ly 60Z is sought.
Such one-co~ponent polyuIethane adhesives cont~n ~er~inal ~CO groups and
a~e gene~ally called isocyanztopolyurethanes ~ Such isocyana~opo~yu~ethanes,
also E~now~ as prepolymers or preadducts, can be prep~ed ~th a s~oLchlo-
metric polyisocyanate e~cess, startlng ~oth ~ram lo~- ahd also hi h molecular
hydro~yl polyeste~ polyol~, as well as the correspondl~ hydroxyl polyether
p~lyols. The poly~ socyanate excess a~d f~nctlonality o~ ~he star~in~ ~at-
erlals mus~ be such th2t the ~ealing o~ f~nls~;ng of the material edges or
surfaces leads to a s~tlsf~ctory strength, durab~lity and elastlclty and i~
particular an adequate stora~e ~ability o~ at lea~t s~x months al e.g. Z0~C,
w~hilst still ensur~g a rapid curi~g of the isocyan~opolyuret~ane followi~g
applicztio~ 3igadva~tages ~lth ~c~ solvent-diluted Lsocya~te polyure~h-
ane prepolymers are the unpleasant~ smell, the toxicolo~ical ob~e~tio~-
abillty, the solve~t e~issions, the curi~g reaceio~ delayed by the solve~ts
Amended sheet
CA 02218104 1997-10-10
~k~o~ and proble~ti~l e.~. in the edge sealing of ehipboards by solvent
retention ~ the wood materi~l~ a~d the r~latively high e~ergy ~hich ~ust be
used in orde~ t~ dry znd further process such ~inished ch~pboards w~ln an
e~ouomlc time period. ~he ¢u~ing reaceion takes pla~e in t~o stages, on the
one ha~d by evapor2ting t~e sol~e~t and on t~e other by t~e action of at~os-
pheric humidity~ ~he curi~ speed is essentially depe~den~ on the mo~sture
coLtent of the m~terial ~d the ambient air. ~2 is produced as a byproduct
and as the end p~oduct ~re obtained crossli~ed polvurethane ~iurets. Fl~-
ally, the t~us finishet surfaces ~st be workable, e. g. ~y gr~nding,
polis~ing, etc.
~he proble~ of the inve~tion i~ to for~ulate a Co~positiOn for a solve~t-
free, lo~- vl~cosity ~50 to 120 m~asl2a~C~, maisture-curln~ isocyanatopoly-
uretha~e prepol~mer, which has an opti~u~ ~e~ting and penetration behaviour
with respect to wood and ~ther porous materials with a rela~ively short
curing time and i~p~oved ~t~rage st~bility. It ts a ~urther pr~blem of the
in~ention ~o impro~e the ~ech~i~ai characteristies of the thus ~reated
~a~er~als, such as the sh~l~kage a~d swelling cha~acterlsti~s under the
actio~ of moisture, transverse teusile, compressive, be~ding ~d tenslle
st~ength, ~hi~st creatîng an ad~esive ~ase for adhesives, coatlng ma~erlals,
etc. o~ ~e thus t~ea~ed ~aterials. ~s a f~ctlon of the lntended use, the
s~face ~ished ~t~ the prepo~ymer ~ust be -water diffusion-tl~ht or wa~er
dif ~usibLe.
According to the inventlon, this prob~em l$ solved by a polyurethane p~e-
polymer ~ompos~tio~ ~lth the ~ollow~n~ formulation
a polyuret~ane prepoly~er of
a) organlc polylsocya~ates.
b) polyols from the group of hydroxyl polyester polyols, hydroxyl polyether
pol~ols or t~ei~ m~xed polyo~s, s~ch as hydroxyl polyester polyether
polyol,
c) orga~c natural subs~ances wi~4 at least one hydroxyl group, a carboxyl
group, an e . te~ group or at least o~e conjugatable double band7
and as ~urther compone~ts
d~ phosph~tes as marklng agents,
Amended she et
CA 02218104 1997-10-10
e) v~cosity sta~ilizers~
~) accelera~ng ca~alysts for ~u~ing the prepolymer from the ~oup of
or~a~iC a~d metallorganic ~ml~es~
A~ ~olyiso~yanates accord~ng to feature a~ are ~n partieular sui~able
aliphatic, cyclozliphatic and ~rcm~tic dii~ocyan~tes. ~re~erence is ~iven
to tke use of those of genera' formula X(~C0)2, ~n ~hich X ~ta~ds for a~
allphatic hydroca~bon radical with 4 to ~ C-atoms ~ cycloalip~atic hydro-
carbo~ radical w~t4 6 to 15 C-ato~ or an aro~atic ~y~rocarbon ~th 6 to 15
G-2so~s .
Pre~erred aromatic~ ~liphatic or cyclo~llphatic diisocy~na~es are 2,4 and
2,~-toluyle~e dilsocyana~es or their isomer ~ixtures, 4,4'-d~phe~yl methane
d~lsocyanate and 2,4'-diphcnyl methane diisocyanate~ tetra~e~yl xylylene,
di~socy~te, isophorone dlisocYanate, 1~6-he~ane di~socyanate, ~1Z~4
and Z,4,~-trl~ethyl he~e~ylene di-socy~nate, ~yclohexane diisocyanate.
methyl ~yclohe~ane d~isoc~n~te, preferably 4,4'-dip~enyl me~hane diisocy-
anate wl~h up to 80h 2~4'-diphenyl methane d~isocyanate Such a ~lxture
ca~ have a density o~ 1.0~ to 1.20 ~/cm . Prefere~ce ls ~iven to che use of
a~ lso~er ~lxture o~ diphenyl methane-4,L'-dl~socyanate a~d dlphenyl me~ha~e-
Z, 4~ -~iisocyanate wt th a free ~1~0 content of approxi~ately 30,0 .
As polyols according to feature b~ ~re suitable ~o~ or high molecul~r weight
polyester ~dlor polyether polyols of ~olecul~r ~eight 200 to 1000. For
specif~c applications po~yether es~er or polyecter ether polyols have proved
satisfactory to a li~ited egte~t and are obtalne~ by the alkox~latio~ of
carbo~ylic acids or Polyesters or by the c~dens~tlo~ of polye~hers with
polyfu~ctional carboxylic acl~s. ~o~e~er, s~id formul~tions only m~intzin
t~eir low YiSCosit~ state for a rela~i~-ely short time (4~ ~o 1~4 hours),
~o t~at ~peedy proees~i~g is "ecessary. P~eference is given to polyols ~ith
molecular weight betwee~ 700 and 3000. They are prepared by reacting
epoxides ~h alcohols. ~lcohcls w~hich can be used are e.g. ethylene
glycol, diethy~ene glycol, propyle~e glycol, g~ycerol, trl~ethyl propane ~nd
pentae~ ritol. ~s epoxides are suitabie e.g. e~y}ene ox~de, propylene
~xlde, ~ut~l o~d~, sty~ene o~lde, cyclohe~ane oxide or epichlorohydr~n.
~e~ra~ydrofuran c~ ~e used i~ place of an epo~ide.
A~ended sheet
. . . _ . _ _ . . , , _
CA 02218104 1997-10-10
3 (A)
Besides polyols, according to feature c~ use is ~ade of ~atural substa~ces
w~th a~ leas~ one hyd~oxide ~roup, a carbo~yl group, an escer group or a
¢onjugat~41e dou41e bond, such as e.~. rosins a d castcr oil. P~efere~ce ls
given to ros1ns ~i~h a~ least one methyl ester gr~up wlth 1 to 5 conjugat-
able double bords, ~hich can be used durl~g Che additio~ reactio~. The acld
nu~ber of suc~ compo~ds is ldeally bèt~ee~ 0.5 a~d 50, prefe~ably bet~een 2
and 20 mg ~OH/g.
~e~ded sheet
CA 02218104 1997-10-10
-- 4 --
As ~arklng ~gents accord~ng to feature d~ hich prevent a sudden viscosl~y
ri~e durlng t~e Polyaddi~ion reaction o~ diisocyanate ~mth the polyhydroxyl
compound to the lsocya atopoly~retha~e prepolymer, but do not i~alr ~he
polyaddltion reaction, use is made of es~ers of phosp~o~ic 2cid, preferably
h~vl~g a refraetive index of 1400 to 1~20 and a bolll~g po~n~ of 75 to 85~C
a~ 5 mbar. ~rlet~yl phosp~ate i5 partlcularly effeotiYe. ~hese addltives
~o ~ot prevent t~e polyaddition re~ion and are characterized by thei~
flame-retard~ng ~aracteristics.
Fa~ t~e viscoslty stabilization of the prepolymer (~eature e), ~an be used
on the one hand bif~nctional, aro~tic dilsocyanates, p~eferzbly Z,4 and
2,6-toluylene dlisocyanates. a~ well as thelr lsomer mixtures and on the
other addlt~ves of organic compounds ~uch a~ 4-methyl dloxola~-(2)-one o~
n-al~yl be~ze~e, ~hich co~tribute to v~scos~ty ~tabil~zatlon for several
months.
To accelerate the ~eaction of the d- lsoeyanates lt ls p~ssible to use co~-
ventioual, ~O~L ca~a~ysts ~fe~ture .~, suc~ as dibu~yl till dilau~ate~ tin-
II-o~toate or ~mines of the gcneral emp~rical form~la C12~24~203 or those of
t~e gene~al empiri~l fonmula C5~14N2 or C6~10N2. ~refera~ly use ls m~de of
n~etallic a~lne eurin~ a~e~s. namely o~ a mlxture o~ 60 ~o ~0~ of the
hî~her valence and 4~ to lOX of the lower vale4ce ammne. Good resul~s have
llso 4~e~ obtzi~ed wlth ~ixtures of the aforemen~ioned me~alorganic com-
pounds 2nd organic ~mines.
A fi~al viscoslty between 2S a~d 70 m~as is obtai~ed ~lt~ the aforeme~ioned
~ompo~l~io~. ~u m2~y other aPPlications, partlcularly ~or the appl~ca~ion,
coat~, e~¢., a higher final viscosity is desi~ed~ I~ order to illcre~se
the ~is~oslty e.g. to 120 m~asl~0~C, i~ is possible to bi~d isocya~ate sem~-
prepolymers ~ith a free ~C0 content of 5 to 20 and preferably 7 to 12~ ln
the polyaddltlo~ reacticn. ~he viscositY re~i~s stable for 6 to 18 month~
w~th a m~ di~e~enoe o~ 10~.
Ad~-antageously flame-re~rding agent~ ~re added to ~he prepoly~er and ~s .
such have proved p~rticula~ly satisfactory p~o~phoric acld polyols ~ith a
phosp~orus ~raction of 5 to 3~ (m~m~, prefer2bly 10 to 20 ~mlm~.
_ . . . . . .... . . . _ _ _ _ _ ... . . ... . _ _
CA 02218104 1997-10-10
Il order to reduce o~ preve~t moisture a'osorptlon, preferably ~ols~ure trap-
p-ng agen~s sre added, Mo~oeyclic, bifunctional o~azolldine has proved
particularly ~uitable. Oxazolidi~e also ser~eS as an a~tifoa~1n~ agent and
as such h~s g~eat signif1cance withi~ the scope of the ~rese~t i~ventio~.
lt prevents ~he fo~ f~rmatio~ ~hich i~ ot~eFwlse observed on ~pply~ng P~R
prepoly~ers ~aking ~t necessary ~o scraPe the appl7' ca~ion several ~i~es,
w~ich leads to a correspo~ m g mater1al loss. ~rough the suppresslon of
foam format~on and co~sequently bubble formatio~, the oxazo~ldi~7e simul-
taneously has a flame-retard~g a~ion
Co~vent1o~al polyur~~~ane prePol~er5 are d~ff1cult to ~-~r~ ~ollo~ng curin~,
because ~elr el 2~tic~ is e~cessive and the work7ng ~ools, e.g. a~rasive
paper~, gr~ding ~-heels or Polishing devices ve~y rapldly become clogged and
ineffectlve. Accordin~ to the inve~tio~ th~s is avoided i~ tna~ metal-
organ~c ~alts are ~d~ed to t~e prepolYmer, nzmely tho~e of ~ar.boxylic acids
o~ empirical formula C~0~0~2 to C22H~4~2' P 18 ~6 2
~e lo~ Viscosl;y polyurethane ~o~ul~tions accordi~g ~o the l~vention are
s.l~able ~0t o~ly for the fi~ls~ or ~ealing o~ ~orous sur~a~e~ ~ut al~o
25 adhe~ives, as reactlve ~hinners or dllue~ts for t~e most ~aried Poly-
ure~hane ~ompo~nds or ~orm~la~icns and as pri~ers far dye~, v~nLshes,
lacq~ers, plastics a~d ~ther materl~ls.
hxample~
The followil~ ~eaniugs are attributed to the a~breviations ~sed ln the
~ollo~ing examples~
p~T 4,4' or ~4'-diphenyl melhane dlisocyana~e
P~ polyetherpoLyol with a molecul~r ~eight of 700 to 3C00
~atural resan ~ased on rosin e~ter of acld nu~ber 5 to ~ mg
~OH/g
KA~ Am~ne acceler~tor
CA 02218104 1997-10-10
-- 6 --
MARX Phosphate a~ ~ar~ing agent
STAB1 ~oluylene diiso~yanate ~DI) as sta~ilizer
STAB2 ~-a}kyl benze~e ~s stabillzer
SEMI Polyure~hane semiPrePol}~er ~ith a visco~lty of 70G0 to 1200
~Pas as a viscos~ty regnl2~Qr far sett~g a hi~her vlscoslty.
Exa~ple ~ ~lo~ viscosi~y P~R prepo,y~er ~rth a ~iscosity ~f 50 mPas/20~C)
MDI 5~A~00
P~D 16.620 ~
N~ 8.310 g
~AT 0~008 g
MA~Y~ 8.31~ g
SL~B1 0.2~ g
AB 2 8.21~ g
~he ~I is placed ~ a do~le-~alled, rool2ble reactor, the ra~ material-
te~perature ~ot exceedi~g 22~C or droppin$ bela~- 18~C In a premlxi~g con-
tainer premlxl~g takes plaee of the de~atere~ ~ED (~-ate~ c~nten~ m~x 500 ppm~
and the ~ 150 de~atered to ~he same ~imum w~ter content) unt11 a st~eak-
free, homogeneous polyol m~ss is obtai~ed. The polyol ~ass, which should be
~n ~he s~e temperature ran~e as t~e ~P~ is t~en added slo~ly, acco~pa~ed
~y const2nt ~tirring a~d te~perature co~trol tc the isocya~te. The mlxl~g
reactor is advantageously e~acuatèd to approximately 150 m~ar. After
m~ing the polyol Lraction into the isoc~anate~ ehe acceler~tor is a~ ed.
As soo~ as a~ exothér2ic te~perature of max 35~~ is reached, the ~ar~ng
~e~t is added to the wi~ure. wsich is ~ooled to belo~- 2~'C. I~mediately
znd wh~lst e~clud~ng at~osp~erlc h~ dity, the ~tab~liz2r 1 CTDI) is added,
~xed in in stre~k-free ~an~er a~d l~m~ tely subseque~tly 2ixed with the
st~bl I ~ 7-~r 2 a~d thoroughly ~tirred ~r at lea t 5 to 10 minutes. The
vl~o~ity ~o~trol ~ust ~ive 3S t~ 3~ mPas/20~C and a sueoessful reaction ls
reve~led by a pale yellow, stre~k--'ree, flake-f~ee, transpare~t soiution.
~he ~hus o~ai~ed ~R prepolymer is le~t to s~an~ 'ar 2h h, ~hllst ex~lud~ng
CA 02218104 1997-10-10
a~mosphexic humidi~ and at a storage ~e~perature of approxi~tely 20~C.
~he subseque~t ~lseos~ty meaSure~eht must give apFro~mately 50 ~Pas/20~C.
E~ample 2
~DI 46.000 ~
P~D13 150 g
6.~70 g
~T 0 0~6 g
~ARK 7.670
~I 19.755
~ABZ 6.570
S~AB1 ~.21~ ~
I~ add~tion to example 1, 2n ~ socyznate semipolymer (SEMI) is added toincrease the f~nal vlscosltv. As in exa~ple 1, the MbI ls placed ~ a
double-~alled, coolable re~eor and the r~w ~2~erial tempera~ure must ~at
d~op below 18~C and must ~ot axceed ~2~C. I~ a pre~ixing container pre-
mix~g takes pl~e o~ ~he dewatered PE~ ~ater coRte~t max 500 ppm) and the
lso de~atered ~o t~e same ~zter co~tent) u~ll a s~reak-free, homogen-
eolls polyol mass ~s obtai~ed. ~ubsequently the pclyol ~as~ is slo~Tly added
to the isocyana~e accompa2led by con~t~nt s~irri~g and maint~in~ the
afore~entioued ranga. ~d-vTantageously the mi~ing reactor is evacua~ed ~o
zpproxl~ately 150 ~a~. As soo~ as the po~yo1 fraction is intermlxed ~n the
isocyanaee, the acceler~tor is added, ~ut only i~ a m~ nm exothermlc state
of 35~C is ~ot reached wlt~l~ 20 minutes. Other~ise the accelerator quan-
~ity ca~ be added. If the accelerator suppl~ lead~ to the exothe~mlc temp~
erature of approxl~ately 35~~ ediate mlxin~ with the m~king z~ent ta~es
place ~nd t~e mlxture is cooled to below 2~~C. Accompanled by slaw stirring~
the semipoly~er wit~ a viscositY o~ 7000 to 12000 ~Past20~~l prefera~ly
10000 mPas +/- 5~0 mP~ ~S stirred in. As soo~ as a mLxture v~scosity rise
is Lndicated by the process ~iscosimeter installed in or o~ the reac~o~.
i~me~tely mas~ing take~ place w~th the stabilizer 2. On re~ing a homo-
ge~eou6 ~lx~ure ~he T~ can be ~dded, ~h~lst e~cludlng a~mospheric ~u~idlty.
A~ter 10 min -~irri~g a visco~y C~sta~cY o~ approxl~ately 120 mPas~20~G
is re~c~ed. ~ny vis~o~ity correctlo~s a~e performed after 24 h. I~ the
CA 02218104 1997-10-10
cas~ o~ inadequate viscosity ret~cke~n~ can ~a~e place ~t4 ~he se~i-
polymer, whereas lf the ~iSCosLty is too high the mlxthre ls diluted a~ i~
example 1. The correc~io~s sho~ld ~ot ~e more t~an 5 ~t.~ ~ased o~ ~e
~otal ~xture, ~eeause other~se the vmscosity stabilitv decreas~s.
~isCosit~ as a function of tl~e at a tes~ te~pe~ature of 20~C:
~e~t tlme 2xample i Exa2ple 2
l~medi~tely after p~eparation 30 ~0
AIter 3h 33 120
After 5 h 37 120
After 24 h 50 120
After 43 h 50 120
After 144 h 50 123
~fter 432 h 50 125
Af~e~ ~5~0 h SS 125
A~ter 10000 h 55 13~
0~ c~ecklng the cu~i~g time the fol~o~g results were o~ e~ compared
wi~h a one-compone4t, msistUre-curl~ ~ol~lreth2ne prepolymer di~uted ~t~
solve2t ~toluene) wi~ a s~milz~ accele~aeion and a solids co~tent of ~0
(herei~after called LM-P~R):
Ex~ple 1: Af~er 12 to 24 h 80~ of the ~i~al s~reng.h and a~er 72 h
10~ of the fi~al strength is rea~hed. ~o~ever, the pro~nct ca~ be mecha~
i~ally further worked after 1~ to 24 1 (ac a fu~ctiou OL the atmospherlc and
~aterlal moisture co~ten~, ~s ~e~ as tne ProcessLng temperature~, e.g. by
grlnd~g, calibrating~ ~rl~mi~g the sealed chipboard or coating ~he fi~ished
materlal surface.
~X-~R; Only a~ter 18 days ls 80~ of the final stren~th and after Z8 days
lOOX of the f~nal strength reached. The storage te~perature i~ ~ 20~,
emp~rica~ly 35 to 40~C.
A ~ate~ia~, such as e.~. ~h~pbcards with a bul~ densi~y bet~een 400 and
CA 02218104 1997-10-10
_ 9 _
800 kg/m3, directly after the c~ring of the polyureth~e prepolyme~ accord-
ing to example 1 on ~he chipbo~rd ~ave neit~er a swel~ing nor a shri~kage
effect. Thus~ tnere is no ~eed to su~sequen~ly callbrate such a chipboard.
A~ opposed to this, a ~ s~stem ~as described herein~efore~ has ~ ~hrlnk-
age effect of on average Z~ o~ the board thick~ess. In addit~on~ a co~mer-
~i~lly available ~ter glass ~yste~ has a swell~ng effec~ of on avera~e
11~. Such baards must be reworked, ~-h~ch Lnvolves additional costs.
Example 3
M~I 60.940 pb~ (p2rts b~ weight)
PEP 14.320
NE 5.730
FS 1.430
0.010
~AR~ 8.Q50
ST~Bl 0.2~0
ST~B3 0~40Q
S~AB~ 7.160
FF L.720
Total lOQ.OOQ pb~- (parts ~ elght~
~he followlng meanlngs are used:
FS fireproofi~g a~ent phospho~us pol~ol
STAB~ fiame-~etarding stabi~izer ~polyslloxane)
FF ~ois~ure trappi~g agen~ and antifoam~ng age~t
MCS carboxylîc acid metal salt
~he sa~e procedure as i~ e~ample 1 i adop~ea, but the FS is siowly added,
aceompanled by st~rr~n~, at a low speed o~ the polyol mass (compr~si~g PE~
and ~H), in s~ch a way that ~o streaks are ~ormed. If the ~S is added too
rapidly, a2 nndesired ir~compatibllity with the rem~ining polyol mass ~hust
be e~p~cted. In t~s case the polyQl m~ture must be reprePared.
CA 02218104 1997-10-10
- 10
~he STAB3 is externally prem1~ed ~n th~ STAB2 and together, following the
addition of STABl and after a correspond~T stirring tlme are subseouently
mixed. After a sti~ring tl~e of 5 to 10 m~nutes, the FF is
supplied, ~hil~ e~cludi~ atmospheric h~mi dl~T~ and o~ce a~aln ~tlrring
e~kes place at z ~lo~ speed for min 10 m~nu~es. It must be ens~red tha~
excessi~ely vigorous stirri~g does not ~ntroduce bubbles.
The same process procedure ~lth the parameters af e~ample 2 leads eo a
hlghe~ ~inal viscosity.
E~a~le 4
prepol;mer accordl~g to example 1 98 pbw
~CS 2 pb~T
Total 100 p~
MCS ~n ~he form of a ~i~e po~der, at the e~ of the pro~ess is dispersed ln
a hlgh-speed dissol~er until a lump-free, ~omo~eneous, f~nely dispersed
mlx~ure is obtai~ed, w~h ~as a mil~y colo~r.
~e prepoLymer obtained ca~ be mechanica~Ly re~-orked extremely ~ell, e.g. by
gri~din8 or polishin~.
~he same proces~ procedure ~ith the para~eters of e~amples 2 and 4 leads to
a prepolymer with a~ l~creased flnal ~iscosity.
